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Additionally, it can display the total consumption which is the most useful characteristic for the purposes of this work. The most relevant technical specifications are reported in Table 4-4.
TABLE 4-4.FLOWMETER TECH SPEC
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FIGURE 4-19.FINAL HYBRID POWERTRAIN LAYOUT
The main difference with respect to Figure 4-18 is the presence of a second DC/DC converter on the battery side of the bus, which transformed the layout into a compromise solution between c and d in Figure 2-8. In this case the buck-boost converter on the FC side keeps the DC-bus voltage to a quasi-stable 36 V, i.e., the rated eDrive voltage, allowing to perform an effective power split control by setting the current of the battery DC/DC. This is easily done with a current-loop bidirectional converter.
More specifically, the controller board should receive in input:
• The eMotor torque or current (according to how the eDrive is designed) to estimate the power demand 𝑃𝑑𝑒𝑚.
• The battery voltage, to perform some basic battery management functions such as keeping 𝑉𝑏𝑎𝑡𝑡 < 𝑉𝑏𝑎𝑡𝑡 𝑚𝑎𝑥.
• The battery SoC, one of the basic inputs for a goof EMS.
The outputs are:
• Direction & magnitude of the bidirectional converter current 𝐼𝑏𝑖𝑑𝑖𝑟, which is set in such a way that the FC current on the DC-bus node is proportional to the desired 𝑃𝐹𝐶 𝑛𝑒𝑡 set by the EMS.
• On/off signals for all the power converters on board and the FCS.
The block diagram for power split control is schematized in Figure 4-20.
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FIGURE 4-20.POWER SPLIT CONTROL SCHEMATIC
The following three converter were chosen for the purpose:
• The LM5170 48V-12V bidirectional converter evaluation module by Texas Instruments mounted on the battery side
• The I7C series buck-boost converter evaluation module by TDK mounted on the FC side
• The I34A series buck converter evaluation module by TDK to supply the FC auxiliaries
FIGURE 4-21.PICTURE OF THE LM5170-BIDIR CONVERTER EVALUATION MODULE
The LM5170-BIDIR Evaluation Module (EVM) is designed to showcase the LM5170-Q1 high performance dual-channel bidirectional controller suitable for, but not limited to, the automotive 48V to 12V dual battery system applications. The EVM can be configured to achieve a bidirectional power converter in the form of either current source or voltage source. The direction of power flow can be
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controlled either by an external command signal (DIR), together with the reference current and the turning on/off signal. Through the onboard interface headers, the EVM can be operated by an external MCU development kit board such as the TI C2000 Delfino LaunchPad XL [38], widely employed within the CARS group. The two channels operate in 180degree interleaved operation, and they evenly share a max dc current of up to 60A in/out the 12V port, which sets the converter’s power rating to about 900W that is plenty for its application on the eCargo. It is equipped with built-in voltage loop control for both low voltage (LV) and high voltage (HV) ports, while it potentially accepts MCU digital voltage loop control through the interface connectors [39]. The most relevant features are summarized in Table 4-5.
TABLE 4-5.LM5170-BIDIR CONVERTER EVALUATION MODULE TECH SPEC
Port Boost mode Buck mode
LV 3 ÷ 48 V OVP disabled 14.5 V (if VL enabled) OVP: 22 V HV 50.5 V (if VL enabled) OVP: 75 V 6 ÷ 75 V OVP: 75 V
According to the voltage rating data in the table above, the mounting configuration was defined (see Figure 4-19). The LV port will be linked to the 36 V DC-bus while the HV port will be linked to the battery. For the converter to work there must always be a non-zero voltage difference between the bus and the battery terminals, a fact which influenced the choice of the battery.
Additionally, the EVM is factory set with over-voltage protection (OVP) circuitry on both power ports, a desirable feature which obstacles the application on the eCargo. As highlighted in Errore.
L'origine riferimento non è stata trovata., the OVP for the LV port in buck mode il 22 V, which is lower than the bus voltage and so not compatible with the future operating point of the device.
Nonetheless, it is possible to change the OVP setting by replacing R18 in the EVM as explained in section 9.2.1.2.11 of the LM5170-Q1 datasheet [40].
As the factory inner loop voltage control is not matching the working voltages of the prototype, it was decided to keep it disabled for the first tests and to leave the duty of keeping the DC-bus voltage at 36V to the I7C series converter, which should be left on as well as the FCS during the early tests.
Concerning the EVM settings, the two and three pin headers should be kept with factory settings, while the following pins in J17 should be for sure connected to the LaunchPad board.
TABLE 4-6.LM5170-BIDIR RELEVANT PINS
Pin Signal Description
1 V48SN HV port voltage sense, i.e., battery voltage sense
5 EN (MASTER ENABLE) EVM enable signal
9 DIR Power flow direction command
11 or 13 ISETA or ISETD Channel current setting (analog voltage or PWM signal)
35 AGND Reference GND for control signals
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The LM5170-BIDIR was modeled within the FC hybrid eCargo model (Figure 4-1) through a Simscape bidirectional DC-DC converter block connected to the DC-bus and the battery model via electrical conserving ports. The block was initialized with parameters from the EVM’s datasheet [39]
that are reported in the table below.
TABLE 4-7.LM5170-BIDIR MODELING PARAMETERS
Switching device Averaged switch
On-state resistance 0.001 Ohm
Protection diode
Forward voltage 0.8 V On resistance 0.001 Ohm Off conductance 1e-5 Ohm
LC parameters
Inductance 100 μH
Inductor series resistance 0 Ohm
C1 470 μF
C2 100 μF
R1 0.4 mOhm
R2 0.4 mOhm
The block receives the gate physical signal, i.e., the Simscape equivalent to the PWM signal sent to a MOSfet’s gate, which is set to “modulation waveform” so the model can act as an average-value converter. The signal’s duty cycle is set by a PI controller which was tuned via Simulink’s PID tuner tool [30] to obtain performances close to the ones described in the EVM’s datasheet.
FIGURE 4-22.LM5170-BIDIR MODEL
Moving on, the converter model i7C4W008A120V-003-R belonging to the I7C series by TDK was selected for the FC side. It is a non-isolated step-up / step-down converter ideal for generating additional DC output voltage up to 300 W from a single output 12V, 24V or 48V DC power supply.
The highly efficient i7C series accepts a very wide DC input and has a wide output adjustment range
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[41]. For the eCargo application the corresponding evaluation module was selected because it incorporates the required external components to ensure the complete product functionality, such as fine output voltage trimming via trimmer pot VR1 [42].
FIGURE 4-23. I7C4W008A120V-003-R EVALUATION MODULE
The most relevant features are reported below
TABLE 4-8. I7C4W008A120V-003-R EVALUATION MODULE TECH SPEC
Type Buck-boost
Input voltage range 9 ÷ 53 V
Output voltage range 9.6 ÷ 48 V
Output current (max) 8 A
Output power (max) 300 W
Efficiency 97%
As shown in Figure 4-20, the converter should be piloted by the LaunchPad board via an on/off signal, however this version can manually be turned on/off via the S1 switch present on the evaluation module [42], which is consistent with the need of keeping the FC on during early tests.
This part was modeled on Simscape through an average value DC-DC converter block which is connected to the bus and the FC via electrical conserving ports and reads as only input the converter efficiency. It is controlled via a duty cycle signal set by a PI controller tuned via Simulink’s PID tuner [30] trying to match as much as possible the information on the converter’s response from the datasheet.
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FIGURE 4-24. I7C4W008A120V-003-R MODEL
Finally, the FC controller will be supplied by another converter, the i3A4W008A033V-001-R belonging to the i3A series by TDK Lambda already installed on its evaluation module. It is a non-isolated DC-DC step-down converter that is are ideal for creating additional output voltage rails from a single output DC-DC power supply including battery sources. The highly efficient i3A series accepts a wide DC input and has a wide output adjustment range, which is made easy by trimmer VR1 welded on the evaluation module. Output trim, remote sense and negative logic remote on-off comes as standard features [43], [44].
FIGURE 4-25. I3A4W008A033V-001-R EVALUATION MODULE
The most relevant technical specifications are reported in the table below.
TABLE 4-9. I3A4W008A033V-001-R TECH SPEC
Type buck
Input voltage range 9 ÷ 53 V
Output voltage range 3.3 ÷ 16.5 V
Output current (max) 8 A
Output power (max) 100 W
Efficiency 96.5%
As shown in Figure 4-20, the converter should be piloted by the LaunchPad board via an on/off signal, however this version can manually be turned on/off via the S1 switch present on the evaluation module [42], which is consistent with the need of keeping the FC on during early tests.
It was not really modeled on Simscape but his efficiency was considered by means of the gain in Figure 4-15.
This chapter ends with the proposed testing layout for the powertrain architecture described so far (Figure 4-26).
FIGURE 4-26.POWER-SPLIT TESTING LAYOUT
In particular, the aim of this testing layout it to gain a deeper understanding of the working principle of the TI bidirectional converter and make sure that it would work on the prototype. The layout relies on a bench power supply of at least 200W simulating the FCS (on the left in Figure 4-26) and on a programmable electronic load which simulates the eMotor power demand on the DC-bus. The latter should be programmed with the motor current demand over a reference cycle, which can be easily extracted from the Simscape simulation results, while the power supply should output a constant 36V voltage and have datalogging capabilities for recording the power output. If this is not possible, a current-voltage sensor should be added downstream to fill this purpose. The TI converter should be installed in the same conditions as in the future prototype and should be controlled in the same way.
The only difference concerns the power demand at the bus which should be calculated from the
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current sensor in the picture, unless a way to program the LaunchPad synchronously to the electronic load with power demand data is found. In the pictures further details about testing can be found.